FIG. 1 shows an example of antenna configuration for use for portable mobile wireless devices (referred to as portable mobile communication terminals or simply portable communication terminals) typified by portable telephone devices and mobile wireless devices.
FIG. 1 is a configuration diagram of a conventional antenna apparatus. In this drawing, feed point 11 feeds antenna element 12. Antenna element 12 has an arbitrary shape, which may be linear, helical, and flat, and radiates electric waves when fed. Ground plane 13 is a circuit board or the like. The length of the length direction of ground plane 13 varies depending on the frequency band of the system that is used and the models of mobile telephone devices and is about ⅜ wave length in the 800 MHz band.
When an antenna apparatus configured such as above is used, it occurs that the body absorbs electric waves and becomes an obstacle to the electric waves. To quantitatively measure the amount of absorption of electric waves into the body,there is a measure of specific absorption called the specific absorption rate (SAR: Specific Absorption Rate), which is the power of electromagnetic energy absorbed per unit mass. In Japan, the specific absorption rate is not to go beyond the level stipulated in the guideline on specific absorption in ARIB STD-T56.
However, the following problem exists with conventional antenna apparatus. That is, when an antenna element is unbalanced-fed, chassis current runs over ground plane 13 while communication is in progress, and radiation starts from ground plane 13 in a gripping position by the body (the hand, specifically) as a part of the antenna apparatus (unbalanced feeding scheme). The electric waves are absorbed and obstructed by the body, which then results in the problem of reduced gain. Moreover, with conventional antenna apparatus, when the specific absorption rate (SAR) goes over the level according to the guideline on specific absorption, antenna loss is increased and the transmission power of mobile telephone apparatus is decreased, which then results in the problem of narrowed communication area.